In order to increase the data throughput of edge users having relatively large inter-cell interference in the cellular network, the study in the Long Term Evolution (referred to as LTE) system R12 proposed the small cell technology which increases the capacity of wireless networks by adding a lot of low-power base stations. These wireless networks can be densely distributed in a certain area to form a cluster, and cells within one cluster may be connected via a non-ideal backhaul link. Because the distance between the base stations is small, interference between the cells can be relatively severe.
As the scenario shown in FIG. 1, there are three co-frequency adjacent small cells 1, 2 and 3 in the coverage of macro cell. The user equipment 1 (UE1) under the small cell 1 is located at the cell edge close to the small cell 1 and the small cell 2, the UE1 will be subject to interference from the small cell 2 and the small cell 3.
Various inter-cell interference coordination methods can be used to reduce interference. In order to achieve interference coordination, the base stations need to obtain each other's interference information, namely, obtain the adjacent cell interference information by measuring the channel state information (referred to as CSI), wherein, the CSI may comprise the channel measurement of adjacent cells, usually the Non-Zero Power Channel State Information Reference Signal (referred to as NZP-CSI-RS) or interference measurements Resource (IMR) can be used to implement the interference measurement of physical downlink shared channel of adjacent cell.
In the LTE R11 protocol, the UE can measure the interference generated under a certain coordination manner through the interference measurement resources configured by the base station side. The interference measurement is performed through interference measurement resources. As shown in FIGS. 2(a), 2(b) and 2(c), the cell 1 performs the interference measurement on the IMR1, and measures the interference in the case that the cell 3 is shut down, and the cell 3 keeps silent at the Resource Element of the IMR1 in the cell 1 so that the coordinated cell 1 can accurately measure the interference.
In addition, the macro cell and the small cell, as well as the small cell and the small cell are connected via the X2 interface to transmit information to be exchanged between the cells. As described in the 3GPP (The 3rd Generation Partnership Project) LTE small cell technical report TR 36.932, the typical delay of a backhaul link including the X2 interface is 2 ms to 60 ms. In order to reduce or eliminate the inter-cell interference, adjacent small cells also need to perform the interference coordination. Realizing the inter-cell interference coordination needs to exchange interference information with the adjacent cells. A backhaul link such as the X2 interface is needed to perform the information exchange between the cell base stations when performing the interference measurement or exchanging the measurement result.
In the R11 CoMP (Coordinated Multiple Points) transmission, the information exchanging required by such coordinated measurement is connected via an ideal backhaul, in which case the transmission delay of the backhaul link does not need to be considered and content of the protocol interface does not need to be standardized. However, when coordinating between cells connected via the non-ideal backhaul link, it needs to rely on the X2 interface to perform the coordinated information exchange. This requires adding the exchanging information required for the coordinated measurement in the backhaul link relevant interface protocol.
In the non-ideal backhaul link, centralized and decentralized inter-cell coordinated information transmission brings some new problems. In the case that respective base stations are not configured with global measurement resources, it may have the problem of resource configuration conflicts. For example, in a decentralized coordinated information exchanging manner, the coordinated measurement process shown in FIGS. 2(a), 2(b) and 2(c) assumes that the cell 3 and the cell 4 perform coordinated CSI measurement. For the IMR1 used by the cell 1 for performing interference measurement in FIGS. 2(a), 2(b) and 2(c), the cell 3 needs to be coordination silent in the corresponding RE. However, as shown in FIGS. 3 (a) and 3 (b), the cell 4 is measuring the interference of the cell 3 at the same position. Since the cell 4 and the cell 1 are not coordinated cells, a conflict will be generated, and the cell 3 needs to be RE silent at the IMR1 location in order to cooperate the cell 1 to measure, while it cannot be RE silent at the IMR1 location in order to cooperate the cell 4 to perform the interference measurement.
The NZP-CSI-RS measurement can also be used to determine the interference situation between adjacent cells, and it also needs to know the ratio Pc of Physical Downlink Shared Channel (referred to as PDSCH) Energy per Resource Element (referred to as EPRE) to NZP-CSI-RS EPRE when judging the interference situation. These resources also need to be cooperated when being configured between the distributed base stations in the case of non-ideal backhaul link. Moreover, due to the delay problem of non-ideal backhaul link, the Pc transfer needs to more accurately reflect the interference situation of the adjacent cell shared channel at different time points or in different frequency resources. It needs to judge the PDSCH interference situation according to the measurement on the CRS for the transmission modes 1-7 of using Cell-specific Reference Signals (referred to as CRS) to perform the channel state information measurement in the LTE, therefore it needs to exchange the ratio PA of PDSCH EPRE to CRS EPRE between the cells.
In the related interference coordination based on the X2 interface, the load indicator, such as mechanisms of downlink Relative Narrowband TX Power (referred to as RNTP), uplink High Interference Indicator (referred to as HII), or Interference Overload Indicator (referred to as OI), can be used to solve the problem of inter-cell interference information indicator. In the small cell interference avoidance issues studied in the LTE R12, it needs to enhance the downlink interference indicator between the small cells connected via the non-ideal backhaul to meet the complex interference avoidance in this scenario.
In addition, the downlink power control method may also be used as a downlink interference avoidance method, therefore it needs to enhance the ICIC (Inter-Cell Interference Coordination) mechanism in the relevant LTE standard, the possible method can be mechanisms such as introducing the downlink HII or OI. But when using the downlink power control as the interference avoidance method, the uplink or downlink HII and OI simply indicate the interference level information, such as, “high interference”, “medium interference” and “low interference”, “high interference sensitive”, “medium interference sensitive” or “low interference sensitive”, and it cannot meet the more accurate downlink power control coordinated information exchanging needs. Through the abovementioned indicator, the adjacent cells cannot obtain quantifiable indicator, such as, what SINR value can be considered as “high interference”, therefore it is inconvenient for the adjacent cells to perform the more accurate adjustment of transmitting power. The adjacent cells need more accurate information when performing power control, for example, they need to determine the transmitting power according to the SINR of the UE in the adjacent cells. Moreover, due to different inter-station distance and other factors, the specific values represented by the interference level information may be different in different cells.